Due to legal regulations, motor vehicles must be subjected to emissions inspections at regular intervals. The emissions test is performed according to a fixed procedure using an exhaust emissions tester, whereby the motor vehicle has to be brought into predetermined operating states for the various individual analysis steps, and be kept in these states for the duration of the respective analysis steps. The predetermined operating states are set by the test personnel in accordance with instructions provided by an analysis procedure, which is typically displayed on a monitor. For example, a predetermined engine speed is set by pressing the accelerator pedal, or the required disturbance variable for the lambda control is applied or removed by pulling off or plugging in an air hose. Predetermined data, including the exhaust gas values, of the motor vehicle being tested are stored and printed out in the form of a test certificate.
Due to legal requirements, enacted, in particular, to reduce the emissions of motor vehicles, the USA since 1996 and the European Union beginning in 2000 have required new cars to be equipped with on-board diagnostic (OBD) systems. These OBD systems, either as a component of the on-board engine control or in combination therewith, detect essential operating variables of the motor vehicle as well as its emissions values using suitable sensors, and detect malfunctions of the motor vehicle by comparing these variables with predetermined recommended variables. In addition to displaying the malfunctions on-board the motor vehicle, the information needed for identifying and repairing these malfunctions must be made available via a diagnostic interface.
Equipping motor vehicles with on-board diagnostic systems will affect the emissions test at least in that current and/or stored emissions-related motor vehicle data will be read out from the diagnostic systems during the emissions test and recorded together with additional emissions test data in the course of the emissions test. This means that the exhaust gas tester must be connected to the diagnostic interface of the on-board diagnostic system.
One object of the present invention is therefore to facilitate a largely automatic execution of the emissions test for motor vehicles having on-board diagnostic systems.
According to one formulation of the invention, this and other objects are achieved by a method of emissions testing for a motor vehicle that has an on-board engine control and diagnostic system and a diagnostic interface. The method includes: performing the emissions test using an emissions tester, executing a program external to the on-board engine control and diagnostic system to control the emissions test, wherein the program generates control commands during the execution, and transmitting the control commands via the diagnostic interface to the on-board engine control and diagnostic system, which sets operating states of the motor vehicle, which are predetermined for the emissions test, as a function of the control commands.
According to another formulation, the invention is directed to an emissions test apparatus for a motor vehicle having an on-board engine control and diagnostic system and a diagnostic interface. The apparatus includes a unit that is arranged outside the engine control and diagnostic system and that generates control commands and transmits the control commands via the diagnostic interface to the engine control and diagnostic system. The control commands are configured to control the engine control and diagnostic system to set operating states of the motor vehicle predetermined for the emissions test.
The present invention is based, inter alia, on the consideration that, in addition to the prescribed standardized, i.e., manufacturer-independent, diagnostic information, manufacturer-specific information may also be read out and/or control commands may be transmitted to the engine control via the diagnostic interface. Accordingly, according to the present invention, control commands are generated externally of the engine control and diagnostic system of the motor vehicle, preferably in an exhaust gas tester or in a controller connected thereto, and transmitted via the diagnostic interface to the engine control arrangement. This provides a particularly advantageous way to automatically set the respective predetermined operating states of the motor vehicle for the exhaust gas test. The control commands are preferably generated by executing a program located in the emissions tester. The program execution preferably contains information about the prescribed procedure of the emissions test as well as manufacturer-specific information about the engine control of the relevant motor vehicle.
Preferably, the system automatically registers the operating states through which the motor vehicle passes during the emissions test, while at the same time registering the emissions values themselves.
In order to ensure that the emissions test proceeds in an orderly manner, the emissions test and/or individual analysis steps of the emissions test are advantageously initiated upon reaching various given operating states. Preferably, it is detected that the various operating states to be set have been reached on the basis of the data obtained from the motor vehicle during the emissions test. At least a part of this data may be read out from the engine control and diagnostic system via the diagnostic interface. In addition, it is possible to register selected data from the motor vehicle in other ways. For example, the engine speed may be registered via the AC voltage part of the vehicle system voltage of the motor vehicle or with the aid of vibration, noise, or magnetic sensors attached in the vicinity of the engine.
By way of example, a predetermined operating state of the motor vehicle to be set in the course of the emissions test may be defined by a predetermined engine speed at a predetermined operating temperature. The operating temperature may be obtained in this case by way of the coolant temperature, information on which may be retrieved via the diagnostic interface. The engine speed may be set directly using a control command transmitted to the engine control, as is performed, for example, within the engine control upon setting a fixed traveling speed for the motor vehicle (cruise control). However, it is also possible to influence the engine speed via an appropriate control command to change the throttle-valve position. In order to be able to set the various individual operating states of the motor vehicle in a defined way, data characteristic for the operating states, for example the engine speed, may be obtained from the motor vehicle. The control commands generated by the system can then be adaptively changed as a function of this data, for example by changing the throttle-valve setting to adjust the current operating state to the desired, i.e. set-point, operating state. Here as well, the data may be read out via the diagnostic interface or registered in some other way from the motor vehicle.